Tim Marshall

Diplomatic Editor

Zed always knew the Syrian secret police would come for him, he just did not know the date. It was December 15, 2012.

Zed, committed to peaceful change in Syria, has been one of the bravest and most outspoken activists in the opposition movement, and one of the few prepared to show his face on the foreign media.

Last year he told me: "I know eventually they will bring me in, but what can I do, we have to change this system by peaceful means."

And then last month he stopped responding to emails, and calls to his mobile went unanswered.

When I was in Damascus in December I called a few times. To my shame I did not follow up on his unexplained silence and have found out later than I should that he has vanished into the secret police system.

Zed is the nickname of 38-year-old Dr Zaidoun al Zoabi, a dean at the European College in Damascus.

It is thought he is being held in the notorious "Building 215" in Damascus along with his 22-year-old brother Souhaib al Zoabi who is a medical student.

Their families are unsure of exactly what has happened to them.

This Christmas was the first he had spent away from his family.

His wife has told their children that he is "travelling". His daughter wrote him a Christmas letter saying how much she misses him.

Image Caption:The Christmas letter written to Dr Zaidoun al Zoabi by his daughter

We first met in a dilapidated tower block in the centre of town. He and an elderly opposition politician were in a shabby office.

The paint was peeling from the walls and the room lit by a single bare light bulb, such is the life of the political opposition.

I was there to interview the other man, Abdul Aziz al Khair, but something attracted me to this burly, humorous activist who was happy to play second fiddle to the established opposition figure.

I left Abdul with our producer Kelvin O'Shea and went off for coffee with this young sardonic firebrand.

We stayed in touch and developed a friendship which both sides kept at a distance, both of us knowing that some of our movements were monitored, but also because I did not want to get too close and thus compromise objectivity.

Zed must have become seriously worried for his safety last year when his mentor, Mr al Khair disappeared on the road to the international airport. He has not been seen since.

The last time I saw Zed was in the early autumn in Damascus. I showed him a report we had made from the city of Homs depicting daily life in the ruined district of Khaldia.

He broke down in tears during one section and then explained he was feeling under immense pressure.

An influential relative had died, leaving him with even less protection than he had, and his wife was pleading with him to give up his activism for the sake of his children.

To my knowledge Zed never supported the violent opposition to the Assad government.

He does criticise the regime, he has participated in demonstrations, but not violence.

He is responsible for driving me around Damascus a few times, he has explained the peaceful activist's strategy, he has even told me in advance about demonstrations, but I've never known him to be involved in what the secret police might legally regard as criminal activity, and he always took great care to distance himself from the armed opposition.

One of several activist groups trying to publicise the al Zoabi's plight is the Syrian Expatriates Organisation which says: "There are serious concerns for the life and safety of Dr Zaidoun al Zoabi and Sohaib al Zoabi in detention.

"Zaidoun is a man of conviction and integrity who worked tirelessly for the cause of freedom and justice in Syria."